1. Field of the Invention
The present invention relates to a glycol dispersion of calcium carbonate. More particularly it relates to a dispersion in glycol such as ethylene glycol of calcium carbonate which is used as a material in the manufacture of polyester which is used as material of especially films or fibers, for the purpose of improving polyester's friction coefficient, wherein the glycol dispersion of calcium carbonate comprises a grade of calcium carbonate having a good dispersion stability in glycol and a good affinity with polyester and glycol such as ethylene glycol, propylene glycol and butylene glycol.
2. Description of the Prior Art
Polyester manufactured today commercially, polyethylene terephthalate (hereinafter called "PET") in particular, has excellent physical and chemical properties, and is being widely used for manufacture of fibers, films and other moldings.
Meanwhile, however, it is known that it has a shortcoming of lacking in sliding property in the process of molding, further processing and handling of manufactured articles, this interfering with the workability and resulting in lowering of the commercial values of the products. And, these troubles are mostly attributable to the high friction coefficient of polyester itself. To overcome such troubles, there have been proposed to date many methods which essentially consist in incorporating fine particles in polyester and imparting a proper degree of roughness to the surface of a molded article to thereby improve the surface sliding property thereof. The affinity between such fine particles and polyester is, however, insufficient, hence there was invariably something to be desired about the transparency and wear resistance of films, fibers et cetera manufactured by such methods.
As means of improving the surface properties of polyester have been hitherto known, among others, the following:
(1) a method of separating out a part or whole of the catalyst et cetera used for synthesis of polyester in the reaction process (internal particle separating-out method)
(2) a method of adding fine particles of calcium carbonate, silicon dioxide et cetera in the course of or after polymerization (external particle adding method)
The internal particle separating-out method (1) has a drawback of having difficulty in controlling the amount and size of particles and in preventing the formation of coarse particles because in this method particles are to be formed during reaction, although the affinity between polyester and particles is somewhat good, for such particles consist of a metallic salt of a polyester component.
The external particle adding method (2), which consists in adding fine particles of an inorganic compound insoluble in and inert to polyester such as titanium dioxide, silica, talc, kaolin and calcium carbonate during or after polymerization, is superior to the method (1) described above with regard to improvement of sliding property, if the particle size and the amount of addition of the inorganic compound are properly selected and coarse particles are removed by classification or the like in advance. However, the affinity between inorganic particles and polyester as an organic substance is insufficient hence separation occurs in the interface boundary between particles and polyester in the course of stretching et cetera, this causing problems about transparency and wear resistance which are still to be solved. For improvement of this affinity between the inorganic compound and polyester, there has been proposed a method of surface treatment by coupling reaction between a silane compound and a titanate compound, but this method, too, has various problems such as the complicated process involved and the fact that the effect attainable is not so good as expected.
Also, for improvement of dispersibility in polyester of such inorganic compound there is proposed a method of preparing glycol slurry of fine particles of the inorganic compound and adding it in the process of polyester manufacture, but there is something to be desired about the dispersibility as well as long-term dispersion stability of such inorganic compound in glycol, hence, when the glycol with such inorganic compound in fine powder form suspended therein is stored for a long period, there are problems of such inorganic compound precipitated to form deposits or hard cakes which are difficult to redisperse or fine particles of such inorganic compound agglomerating in glycol or in the course of manufacture of polyester. The presence of agglomerated coarse particles in polyester can cause yarn breakage in the spinning process, formation of the so-called "fish eye" et cetera and, in particular, drop-out or lowering of S/N ratio when it is used for manufacture of film for magnetic tape, and there has been a strong need for development of fine particles free from formation of coarse particles.